Equivalent deficits in bone mass of the vertebral body and posterior processes in women with vertebral fractures: implications regarding the pathogenesis of spinal osteoporosis

Differing Effects of Zoledronic Acid on Bone Microarchitecture and Bone Mineral Density in Men Receiving Androgen Deprivation Therapy: A Randomized Controlled Trial

Androgen deprivation therapy (ADT) given to men with prostate cancer causes rapid and severe sex steroid deficiency, leading to increased bone remodeling and accelerated bone loss. To examine the effects of a single dose of zoledronic acid on bone microarchitecture, we conducted a 2-year randomized placebo controlled trial in 76 men, mean age (interquartile range [IQR]) 67.8 years (63.8 to 73.9) with non-metastatic prostate cancer commencing adjuvant ADT; 39 were randomized to zoledronic acid and 37 to matching placebo. Bone microarchitecture was measured using high-resolution peripheral quantitative computed tomography (HR-pQCT). Using a mixed model, mean adjusted differences (MAD; 95% confidence interval [95% CI]) between the groups are reported as the treatment effect at several time points. Over 24 months, zoledronic acid showed no appreciable treatment effect on the primary outcomes for total volumetric bone mineral density (vBMD); radius (6.7 mg HA/cm³ [-2.0 to 15.4], p = 0.21) and tibia (1.9 mg HA/cm³ [-3.3 to 7.0], p = 0.87). Similarly, there were no between-group differences in other measures of microarchitecture, with the exception of a modest effect of zoledronic acid over placebo in total cortical vBMD at the radius over 12 months (17.3 mgHA/cm³ [5.1 to 29.5]). In contrast, zoledronic acid showed a treatment effect over 24 months on areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) at all sites, including lumbar spine (0.10 g/cm² [0.07 to 0.13]), p < 0.001), and total hip (0.04 g/cm² [0.03 to 0.05], p < 0.001). Bone remodeling markers were initially suppressed in the treatment group then increased but remained lower relative to placebo (MADs at 24 months CTX -176 ng/L [-275 to -76], p < 0.001; P1NP -18 mg/L [-32 to -5], p < 0.001). These findings suggest that a single dose of zoledronic acid over 2 years is ineffective in preventing the unbalanced bone remodeling and severe microstructural deterioration associated with ADT therapy. © 2020 American Society for Bone and Mineral Research.

A method to develop an in vitro osteoporosis model of porcine vertebrae: histological and biomechanical study

OBJECT

The porcine spine is widely used as an alternative to the human spine for both in vivo and in vitro spinal biomechanical studies because of the limited availability and high cost of human specimens. The aim of this study was to develop a reproducible in vitro osteoporotic vertebral model for spinal implant investigations.

METHODS

Four mature domestic porcine lumbar spines (L1-5) were obtained. An in vitro decalcification method was used to decrease the mineral content of the porcine vertebrae, with Ca-chelating agents (0.5 M EDTA solution, pH 7.4) that altered the bone mineral density (BMD). Lumbar-spine area BMD was evaluated using dual-energy x-ray absorptiometry; spine volumetric BMD and spine geometry were assessed by central quantitative CT scanning to monitor the time it took the decalcification process to induce the WHO-defined standard of osteoporosis. Micro-computed topography provided information on the 3D microarchitecture of the lumbar vertebrae before and after decalcification with EDTA. Hematoxylin and eosin staining of lumbar vertebrae was performed. Both the control (5 specimens) and osteoporotic vertebrae (5 specimens) were biomechanically tested to measure compressive strength.

RESULTS

The differences in area BMD measurements before and after the demineralizing processes were statistically significant (p < 0.001). The results of the compression test before and after the demineralizing processes were also statistically significant (p < 0.001).

CONCLUSIONS

The data imply that the acid demineralizing process may be useful for producing a vertebra that has some biomechanical properties that are consistent with osteoporosis in humans.

Independent and combined contributions of cancellous and cortical bone deficits to vertebral fracture risk in postmenopausal women

Using iliac bone histomorphometry on 78 patients with vertebral fracture and 66 healthy postmenopausal women, cortical thickness discriminated at least as well as any cancellous bone structural index between the two groups. Subjects with a deficit in both cortical and cancellous bone had much greater likelihood of fracture.

INTRODUCTION

Vertebral fracture is often attributed to disproportional loss of cancellous bone, but fracture patients may have deficits in cortical and cancellous bone. Accordingly, we examined the contribution of cortical and cancellous bone deficits, separately and together, to the likelihood of vertebral fracture.

MATERIALS AND METHODS

Iliac bone histomorphometry was performed in 78 white woman with clinically apparent vertebral fracture, 66 healthy postmenopausal women, and 38 healthy premenopausal women. We measured cancellous bone volume (Cn.BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), cortical bone volume (Ct.BV/TV), and cortical thickness (Ct.Th). For each variable, a value of >1 SD below the mean in premenopausal women was treated as a putative risk factor, and its association with the presence or absence of fracture was determined by OR calculated by logistic regression and by receiver operating characteristic (ROC) curve analysis. Subsets of fracture and control subjects were separately matched for Cn.BV/TV and Ct.Th.

RESULTS

All structural indices differed between fracture patients and controls except Ct.BV/TV. There was a weak but highly significant correlation between Cn.BV/TV and Ct.Th in the entire group (r = 0.389, r(2) = 0.151 p < 0.001). Many control subjects had a high value for one of these variables and a low value for the other. Ct.Th., Cn.BV/TV, and Tb.N were all significantly associated with vertebral fracture (ORs, 4.4-5.8; ROC area under the curve [AUC], 0.74-0.85). In subjects matched for Cn.BV/TV, Ct.Th was reduced by 29% (OR, 5.0), and in subjects matched for Ct.Th, Cn.BV/TV was reduced by 27% (OR, 5.0). In patients with deficits in both cortical and cancellous bone, the ORs ( 28-35 ) were much higher.

CONCLUSIONS

Deficits in cortical bone (reduced value for Ct.Th) and in cancellous bone (reduced values for Cn.BV/TV or Tb.N) were equally effective in discriminating between subjects with and without vertebral fracture. With a deficit in both cortical and cancellous bone, the association with vertebral fracture was much stronger. Vertebral fracture is not the result of disproportionate loss of cancellous bone in the patients as a whole, although individual patients may have relatively greater deficits in either cancellous or cortical bone.

Males have larger skeletal size and bone mass than females, despite comparable body size

Gender differences in fractures may be related to body size, bone size, geometry, or density. We studied this in 18-year-old males (n = 36) and females (n = 36) matched for height and weight. Despite comparable body size, males have greater BMC and BMD at the hip and distal tibia and greater tibial cortical thickness. This may confer greater skeletal integrity in males.

INTRODUCTION

Gender differences in fractures may be related to body size, bone size, geometry, or density. We studied this in males (n = 36) and females (n = 36; mean age = 18 years) pair-matched for height and weight.

MATERIALS AND METHODS

BMC, bone area (BA), and BMD were measured in the spine and hip using DXA. Distal tibia was measured by pQCT.

RESULTS AND CONCLUSIONS

Males had a higher lean mass (92%) compared with females (79%). No gender differences were observed for vertebral BMC or vertebral height, although males had greater width and thus BA at the spine. Males had greater BMC and BA at the femoral neck and total femur (p < 0.02). Geometric variables of the hip including neck diameter and neck-axis length were also greater in males (p < 0.02). There was greater cross-sectional moment of inertia, safety factor, and fall index in males (all p < 0.02). Males had greater tibial BMC, volumetric BMD, and cortical area and thickness compared with females (p < 0.01), with both greater periosteal circumference (p = 0.011) and smaller endosteal circumference (p = 0.058). Statistically controlling for lean mass reduced gender differences, but males still had 8% higher hip BMD (p = 0.24) and 5.3% higher total tibial BMD (p = 0.05). A subset of males and females were matched (n = 14 pairs) for total hip BA. Males in this subset still had greater BMC and BMD at the total hip (p < 0.05) than females, despite similar BA. In summary, despite comparable body size, males have greater BMC and BMD than females at the hip and distal tibia but not at the spine. Differences in BMC and BMD were related to greater cortical thickness in the tibia. We conclude that differences in bone mass and geometry confer greater skeletal integrity in males, which may contribute to the lower incidence of stress and osteoporotic fractures in males.

The contribution of reduced peak accrual of bone and age-related bone loss to osteoporosis at the spine and hip: insights from the daughters of women with vertebral or hip fractures

The genetic hypothesis states that a daughter will resemble her mother by about 50% in a given trait because she shares, on average, half her genes. We used this trait resemblance in mothers and daughters to determine whether abnormalities in volumetric bone mineral density (vBMD) or bone size in women with fractures originate in growth or aging. vBMD and volume of the third lumbar vertebra and femoral neck were estimated using posteroanterior (PA) scanning by dual-energy X-ray absorptiometry (DXA). Vertebral volume was estimated as (scan area)(3/2) and femoral neck volume was pi* (width/2)(2)* height. vBMD was bone mineral content (BMC)/volume. The data were expressed as age-specific SD or Z scores (mean +/- SEM). Vertebral vBMD was reduced by -0.98 +/- 0.14 SD (p < 0.001) in 34 women with vertebral fractures, and by -0.36 +/- 0.13 SD (p < 0.05) in their 44 premenopausal daughters. The vBMD deficit in the daughters (relative to age-matched controls) was no different from one-half their mothers' deficit (relative to their age-matched controls). Vertebral volume was reduced in the women with vertebral fractures relative to age-matched controls (-0.77 +/- 0.15 SD; p < 0.001), but not in their daughters (-0.17 +/- 0.13 SD, NS). The 31 women with hip fractures and their 41 premenopausal daughters had no deficits in vertebral volume or vBMD. Femoral neck vBMD was reduced in the women with hip fractures (-1.24 +/- 0.12 SD; p < 0.001) but not in their daughters (-0.17 +/- 0.13 SD, NS). Femoral neck volume was increased by 0.98 +/- 0.30 SD (p < 0.05) in women with hip fractures (relative to age-matched controls) and by 0.54 +/- 0.14 SD (p < 0.001) in their daughters (relative to age-matched controls); that is, about one-half that of their mothers. We propose that women with vertebral fractures have reduced vertebral vBMD because of, in large part, reduced accrual of bone during growth (because the deficit in their daughters was almost one-half their mothers' deficit); reduced vertebral volume in women with vertebral fractures is caused by reduced periosteal apposition during aging (because their daughters have no deficit in vertebral volume). Women with hip fractures have reduced vBMD because of age-related bone loss (because their daughters have no deficit in vBMD) but the increased femoral neck volume is growth related (because their daughters' femoral neck size is increased by one-half as much). The pathogenesis of bone fragility at the axial and appendicular skeleton is heterogeneous and has its origins in growth and aging.

Differences in skeletal kinetics between vertebral and humeral bone measured by 18F-fluoride positron emission tomography in postmenopausal women

We have sought to investigate regional differences in skeletal kinetics between lumbar vertebrae and the humerus of postmenopausal women with 18F-fluoride positron emission tomography (PET). Twenty-six women, mean age 62 years, had dynamic PET scans of the lumbar spine and lower humerus after the injection of 180 MBq 18F-fluoride ion. Plasma arterial input functions (IFs) were calculated from a mean IF measured arterially from 10 women and scaled according to late individual venous activity. Vertebral and humeral time activity curves were measured by placing regions of interest (ROI) over lumbar vertebrae and the humeral shaft. Using a three-compartmental model and nonlinear regression analysis the macroconstant Ki, representing plasma clearance of fluoride to bone mineral, and the individual rate constants K1 (related to regional skeletal blood flow) and k2 to k4 describing transport between plasma, an extracellular fluid compartment and a bone mineral compartment, were measured. Mean vertebral Ki (3.47x10(-2) ml x min(-1) x ml(-1)) and K1 (1.08x10(-1) ml x min(-1) x ml(-1)) were found to be significantly greater than humeral Ki (1.64x10(-2) ml min(-1) ml(-1); P<0.0001) and K1 (3.90x10(-2) ml x min(-1) x ml(-1); P<0.0001) but no significant differences were found in k2, k3, and k4. These findings confirm differences in regional skeletal kinetics between lumbar vertebrae and the lower humerus. These observations may help increase our understanding of the regional differences in pathophysiology and response to treatment that have been observed in sites consisting predominantly of either trabecular or cortical bone. 18F-fluoride PET may prove to be a valuable technique in the noninvasive measurement of regional skeletal metabolism.

Spinous process strength

STUDY DESIGN

Mechanical testing of cadaveric lumbar spines and dual energy radiograph absorptiometry scanning were performed.

OBJECTIVES

To devise a technique to measure the strength of lumbar spinous processes and to determine the bone mineral density of the vertebrae used.

SUMMARY OF BACKGROUND DATA

The spinous process has been identified as the weakest part of the anatomy to which a flexible fixation device can be attached. It was unknown if the spinous processes could withstand the forces applied by the device.

METHODS

A hook was fitted to the spinous process of 32 lumbar vertebrae. A custom-built rig was designed to secure a vertebra to a materials testing machine. A loop of cord was passed over a bar mounted on the crosshead of the machine and around the two bollards of the hook. As the crosshead was raised, a tension was applied to the cord. Each vertebra was tested to failure. The bone mineral density of each vertebra was then measured using dual energy radiograph absorptiometry.

RESULTS

Failure of the specimens occurred by failure of the spinous process, pedicles, or vertebral body. The logarithm (base 10) of the load (N) at which failure occurred was 2.53 +/- 0.3, which corresponded to a mean failure load of 339 N. The bone mineral density of each vertebral body varied between 0.263 and 0.997 g/cm2. A significant linear correlation was found between bone strength and bone mineral density (P < 0.0001).

CONCLUSIONS

Specimens with a bone mineral density in the range of 0.263-0.997 g/cm2 failed at a mean load of 339 N when the load was applied through the spinous process hook of a flexible fixation device.

Cross-sectional and longitudinal assessment of pre- and postmenopausal bone loss with a portable forearm X-ray device: the Ofely study

The aim of our study was to describe cross-sectional and longitudinal bone mineral decrease in pre-, peri-, and postmenopausal healthy women using a monoenergy X-ray densitometer specifically designed for forearm assessement. Measurements were performed on the most distal part of the radius (ultradistal, 55% of trabecular bone and 45% of trabecular bone), and on the distal part (distal, 13% of trabecular bone and 87% of cortical bone). A specific trabecular-rich region of interest (nROI) comprising two trapezoids regions of interest located proximally to the endplates of the radius and ulna was also investigated. From a large prospective study (OFELY study), 455 women were measured once a year for 2 years (three measurements). The proportion of postmenopausal women classified as having osteoporosis (i.e., a T score <-2.5) was 33% for the distal region, 44% for the ultradistal region, and 45% for the nROI. No significant bone mineral decrease was found over the 2-year period in premenopausal women (n = 138). In perimenopausal (n = 48) women, a bone loss of 1% was found at the distal site. In the 269 postmenopausal women, a significant decrease was observed at all sites, ranging from 2.14% for the nROI to 2.68% for the ultradistal part. Bone loss was greater in the first 5 years after menopause in trabecular sites and decreased thereafter. For the distal site, bone loss remained stable during the postmenopausal period. We conclude that this small and portable forearm densitometer is suitable for the diagnosis of osteoporosis, and provides information on the rate of bone loss in peri- and postmenopausal women in trabecular and cortical compartments of bone.

T score of trabecular and cortical bone in normal postmenopausal women

OBJECTIVE

The T score of the cortical and trabecular bone compartments (T score of BMDTrab and T score of BMDCorti) was calculated in healthy postmenopausal women to determine which bone compartment loses more bone mass.

MATERIAL AND METHODS

A total 134 healthy postmenopausal women (mean age 55.1 +/- 6.4 years) and 67 healthy premenopausal women (mean age 36.0 +/- 8.6 years) were studied. Determinations were made using peripheral quantitative computed tomography (pQCT) of the nondominant forearm. The postmenopausal women were divided into groups by years since menopause (YSM): two early postmenopausal groups: < 5 YSM and 6-10 YSM; and two late postmenopausal groups: 11-20 YSM and > 20 YSM.

RESULTS

There was a significant correlation between the T score of BMDTrab and the T score of BMDCorti (P < 0.0001). Both correlated negatively and significantly with age (P < 0.001 and P < 0.0001, respectively) and neither correlated with weight. The Wilcoxon test showed no significant differences between the trabecular and cortical T scores in the overall group of women. By YSM, only the > 20 YSM group showed significant differences (P < 0.005). The ANOVA post hoc Bonferroni/Dunn test showed a significant difference in the T score of BMDTrab by YSM only in the < 5 YSM versus 11-20 YSM groups (P = 0.007) and in the < 5 YSM versus > 20 YSM groups (P < 0.0001). The T score of BMDCorti by YSM differed significantly only between the < 5 YSM versus 11-20 YSM groups (P < 0.0001) and between the 11-20 YSM and > 20 YSM groups (P < 0.005).

CONCLUSION

In contrast with what has been postulated in recent studies, our results showed that postmenopausal bone loss was similar in the cortical and trabecular bone compartments in the first 20 years after menopause. Trabecular bone loss was greater than cortical bone loss in late menopause (> 20 years).

The benefit of hormone replacement therapy on bone mass is greater at the vertebral body than posterior processes or proximal femur

The aim of this study was to determine whether the higher vertebral bone mass in women receiving hormone replacement therapy (HRT) is confined to the trabecular rich vertebral body rather than the predominantly cortical posterior processes, and to determine whether the protective effect of HRT at the proximal femur, a predominantly cortical site, is less than at the spine. Bone mass (g) of the third lumbar vertebra (total, vertebral body and posterior processes, measured by lateral scanning), and bone mineral density (g/cm2) of the femoral neck, Ward's triangle, and trochanter were measured using dual X-ray absorptiometry in a cross-sectional study of 71 women receiving HRT for 5.7 +/- 0.4 years (mean +/- SEM), ranging from 1 to 21 years, 69 age-matched controls, and 42 premenopausal controls aged 20 to 40 years. Relative to untreated postmenopausal controls, total bone mass of the third lumbar vertebra (body plus posterior processes) by postero-anterior (PA) scanning was 0.4 +/- 0.1 SD or 9.6 +/- 3.0% higher in HRT treated women (p < 0.01). By lateral scanning, total bone mass was higher than age-matched controls (z score 0.4 +/- 0.1 SD or 11.2 +/- 3.4%, p < 0.01). This difference was confined to the vertebral body (z score 0.6 +/- 0.1 SD, p < 0.001), which was 17.1 +/- 3.3% higher than in age-matched controls (p < 0.001). Bone mass of the posterior processes was no higher [z score 0.1 +/- 0.1, not significant (NS)]. The deficit at the vertebral body in HRT-treated women, relative to premenopausal controls, was half the deficit at the vertebral body in untreated postmenopausal women (t score -0.7 +/- 0.1 vs. -1.4 +/- 0.1 SD, respectively; p < 0.001) but no less at the posterior processes (t score -1.6 +/- 0.2 vs. -1.9 +/- 0.2 SD, respectively; NS). Similarly, the deficit in the vertebral body in the HRT treated group was half the deficit at their posterior processes (t score -0.7 +/- 0.1 SD vs. -1.6 +/- 0.2, respectively; p < 0.001). In HRT-treated women, bone mass diminished significantly with age at the posterior processes (r = -0.31, p < 0.01), but not at the vertebral body (r = -0.21, p = 0.07). Bone mass diminished significantly with age at the vertebral body and posterior processes in untreated women (r = -0.55, p < 0.001; r = -0.45, p < 0.001, respectively). Bone density (g/cm2) diminished at all femoral sites with advancing age in HRT-treated women. A protective effect was seen at the femoral neck and Ward's triangle, but not trochanter (z score 0.2 +/- 0.1, p = 0.06; 0.3 +/- 0.1, p < 0.05; 0.0 +/- 0.1, NS, respectively). In conclusion, the protective effect of HRT against bone loss at the vertebral body, the site of fracture in osteoporosis, may be underestimated by PA scanning. The greater benefit at the vertebral body, and more modest effect at the proximal femur, suggests that HRT may be a more effective means of reducing the risk of spine than hip fractures.